4-MW direct drive headed offshore
A quick scan of recent news shows that U.S. coastal waters are the next big development area for wind plants. It makes sense to put the largest practical units in the steady winds offshore. GE, for one, says it will apply its experience to the offshore wind industry as it matures, growing from a 1.5 GW installed based in 2008 to a forecasted 30-GW opportunity by 2020. So for having the right turbine at the right time – as the offshore market blooms – the GE 4.0-110 turbine is our Turbine of the Month.
The company says its 4.0 MW wind series platform removes the single most costly failure in turbines, gearboxes, and replaces it with a reliable slow speed generator. GE is able to add this turbine to its portfolio of machines because it bought the developer, Norway’s ScanWind, in September 2009.
A few technical features of the 4.0 MW unit include about a 6-m diameter permanent magnet generator the company says delivers high efficiency at low wind speed. At just 10 rpm, magnets at the rotor tip will be moving at about 188 m/min. The generator’s 20 sections or modules allow replacing a portion of it without a complete removal of the 90-ton unit. Two main bearings transfer axial and bending loads from rotor to bedplate for higher reliability. The unit also sports continuous close-wind tracking to capture more energy. Also important are what it does not have: No yaw brakes or hydraulics.
Through development, installation, and operation of Ireland’s Arklow wind farm, GE has more than six years of experience and an understanding of what it takes to deliver and operate offshore wind turbines. In 2005, 13 direct-drive wind turbines using the same design principles were installed along Norway’s coast. GE reports that the turbines have since accumulated 50 years of equivalent operating experience under some of the most challenging conditions nature can whip up: Salt spray, storms and lightning, winds averaging 9.7 m/s, and temperatures from –25°C to +25°C.
The 4.0 turbine boasts of several maintenance and safety advantages thanks to a spacious nacelle and internal-hub access which means not having to exit the nacelle to access machinery in the hub. The design also offers redundant operation, automatic lubrication, and in–situ repairs wherever possible to maximize unit availability and reduce operating costs.
Lastly, the blades on the 4.0 MW turbines, made partially with carbon fiber, are of the company’s proprietary design. They twist in high wind to soften the impact of gusts, while their airfoil is shaped to increase torque. WPE
